Along with the miniaturization of semiconductor devices, process conditions (process window) for realizing a uniform processing result within a wafer plane through plasma processing have become narrower year after year, and therefore, plasma processing apparatuses are required to control the process conditions in a more complete manner. In order to respond to such demands, apparatuses are required to control the distribution of plasma, the dissociation of process gas and the surface reaction within the reactor with extremely high accuracy.
Currently, a typical plasma source used in such plasma processing apparatus is the high frequency inductively coupled plasma source (hereinafter referred to as ICP). In the ICP, at first, high frequency current I flowing through the high frequency induction antenna creates an induction magnetic field H around the antenna, and the induction magnetic field H creates an induction electric field E. At this time, if electrons exist within the space in which plasma is to be generated, the electrons are driven by the induction electric field E, ionizing gas atoms (molecules) and generating ion and electron pairs. The electrons generated in this manner are driven again by the induction electric field E together with the original electrons, by which further ionization is caused. Finally, plasma is generated via avalanche ionization phenomenon. The area in which plasma density is highest is where the induction magnetic field H or the induction electric field E is strongest within the space in which plasma is generated, that is, the area closest to the antenna. Further, the intensity of the induction magnetic field H and the induction electric field E attenuates by double the distance from the line of current I flowing through the high frequency induction antenna set as center. Therefore, the intensity distribution of the induction magnetic field H and the induction electric field E, in other words, the plasma distribution, can be controlled via the shape of the antenna.
As described, the ICP generates plasma via the high frequency current I flowing through the high frequency induction antenna. In general, when the number of turns of the high frequency induction antenna is increased, the inductance increases and the current drops, but the voltage increases. In contrast, when the number of turns is reduced, the voltage drops but the current increases. In designing the ICP, the preferable level of current and voltage is determined by various reasons, not only from the viewpoint of uniformity, stability and generation efficiency of plasma, but also from the viewpoint of mechanical and electrical engineering. For example, the increase of current causes problems such as heat generation, power loss caused thereby, and current-resisting property of the variable capacitor used in the matching circuit. On the other hand, the increase of voltage causes problems such as abnormal discharge, the influence of capacitive coupling of the high frequency induction antenna and plasma, and the voltage resisting property of the variable capacitor. Therefore, the designers of ICP must determine the shape and the number of turns of the high frequency induction antenna considering issues such as the current resisting property and the voltage resisting property of electric elements such as the variable capacitor used in the matching circuit, the cooling of the high frequency induction antenna and the problem of abnormal discharge.
The ICP is advantageous in that the intensity distribution of the induction magnetic field H and the induction electric field E created by the antenna, that is, the distribution of plasma, can be controlled by the winding method or the shape of the high frequency induction antenna. Based thereon, ICPs have been devised in various ways.
One actual example is a plasma processing apparatus for processing a substrate on a substrate electrode using ICP. An example of such plasma processing apparatus is proposed, wherein a portion or all of the high frequency induction antenna is multi-spiral shaped, realizing a more uniform plasma, reducing the deterioration of electric power efficiency of a matching parallel coil of the matching circuit for the high frequency induction antenna, and minimizing temperature increase (refer for example to patent literature 1).
Another structure has been proposed in which a plurality of identical high frequency induction antennas are respectively disposed in parallel at given angles. One example proposes disposing three lines of high frequency induction antennas at 120° intervals, so as to improve the circumferential uniformity (refer for example to patent literature 2). The high frequency induction antenna can be wound vertically, wound on a plane, or wound around a dome. If a plurality of identical antenna elements are connected in parallel in a circuit-like manner as disclosed in patent literature 2, the total inductance of the high frequency induction antenna composed of multiple antenna elements can be reduced advantageously.
Another example proposes connecting two or more identically shaped antenna elements in parallel in a circuit-like manner to form the high frequency induction antenna, wherein the antenna elements are arranged either concentrically or radially so that the center of the antenna elements corresponds to the center of the object to be processed, the input ends of the respective antenna elements are arranged at angular intervals determined by dividing 360° by the number of antenna elements, and the antenna elements are formed to have a three-dimensional structure in the radial direction and the height direction (refer for example to patent literature 3).
In contrast to the ICP, an electron cyclotron resonance (hereinafter referred to as ECR) plasma source is a plasma generating device utilizing the resonance absorption of electromagnetic waves by electrons, which has superior characteristics in that the absorption efficiency of electromagnetic energy is high, the plasma igniting property is high, and a high density plasma can be obtained. Currently provided plasma sources utilize microwaves (2.45 GHz) or electromagnetic waves of the UHF and VHF bands. In order to radiate electromagnetic waves into the discharge space, electrodeless discharge using waveguides is mainly used for microwaves (2.45 GHz), whereas parallel plate-type capacitive coupling discharge using capacitive coupling between the electrode radiating electromagnetic waves and plasma is mainly used for UHF and VHF.
There is another plasma source that utilizes an ECR phenomenon using a high frequency induction antenna. According to this example, plasma is generated using waves accompanying a kind of ECR phenomenon called whistler waves. Whistler waves are also called helicon waves, and a plasma source utilizing this phenomenon is also called a helicon plasma source. According to the arrangement of the helicon plasma source, for example, a high frequency induction antenna is wound around the side wall of a cylindrical vacuum chamber, a high frequency power having a relatively low frequency, such as 13.56 MHz, is applied, and a magnetic field is further applied thereto. At this time, the high frequency induction antenna generates electrons rotating in the clockwise direction for half a cycle of 13.56 MHz and that rotate in the counterclockwise direction for the remaining half cycle of 13.56 MHz. Out of these two types of electrons, the mutual interaction between the electrons rotating in the clockwise direction and the magnetic field causes the ECR phenomenon. However, the helicon plasma source has various problems and is not suitable for industrial application, since the time in which ECR phenomenon is caused is limited to half a cycle of the high frequency, the location in which ECR is caused is dispersed and the absorption length of electromagnetic wave is long so that a long cylindrical vacuum chamber is required and plasma uniformity is difficult to achieve, and plasma characteristics (such as the electron temperature and gas dissociation) cannot be controlled appropriately since the plasma characteristics changes in steps.    [Patent Literature 1] Japanese Patent Application Laid-Open Publication No. 8-83696    [Patent Literature 2] Japanese Patent Application Laid-Open Publication No. 8-321490    [Patent Literature 3] Japanese Patent Application Laid-Open Publication No. 2005-303053    [Non Patent Literature 1] L. Sansonnens et al., Plasma Sources Sci. Technol. 15, 2006, pp 302    [Non Patent Literature 2] J. Hoopwood et al., J. Vac. Sci. Technol., All, 1993, pp 147